Mostaccioli are dense, dark, nutty cookies shaped like diamonds and covered with a chocolate glaze. The key ingredient to make traditional mostaccioli is vincotto, a syrupy cooked grape must (mosto in Italian, hence their name, mostaccioli), or vincotto di fichi, a thick, slow-cooked fig syrup. Both are very common in the Italian South, usually used to drizzle over Christmas and Easter sweet treats, or, as in this case, to sweeten mostaccioli. You can substitute vincotto with molasses or honey. These cookies are typical of the Southern Italian region, from Campania to Basilicata, from Abruzzo to Puglia. The first time I met them, they were almost hidden in a large tray of almond paste cookies my husband’s aunt had brought us from Lecce, in Puglia, to celebrate Christmas. Even though almond paste is one of my favorite treats, I kept coming back to the spiced, chocolate-glazed diamonds. That was the beginning …